Hello,
The planned order would have a sales order assigned to it, which would contain the configuration data.
The logic could be as below,
From PLAF based on the planned order number (PLAF-PLNUM) get the sales order number (PLAF-KDAUF) and item number (PLAF-KDPOS).
Based on PLAF-KDAUF & PLAF-KDPOS fetch the configuration number(VBAP-CUOBJ) from VBAP.
Pass VBAP-CUOBJ to the function module VC_I_GET_CONFIGURATION as the INSTANCE input parameter INSTANCE = VBAP-CUOBJ.
In the output table CONFIGURATION, you have all the characteristics and their values.
Hope this helps you 
Best Regards,
Ameya Beri